306 CEYLON PEARL OYSTER REPORT. 



in such characters amongst themselves (figs. 1G, 17), the matter is probably of no 

 systematic importance and the whole series may be regarded as one species. 



One point of interest belonging to these specimens from Galle is that, from the 

 circumstance of their attachment to the basket which was put out on April 17 and 

 brought in on May 9, it is known that they grew to a length of 2 centims. and became 

 sexually mature within a period of three weeks. 



This is one of those troublesome species that show no very striking characteristics 

 and yet do not agree exactly with any other species. In external appearance the 

 specimens agree in general with several common species of Ascidia, such as A. prurium, 

 O. F. M., A. obliqua, Ald., A. scabra, 0. F. M., and A. mollis, Ald. and Hanc, but 

 they differ from all these northern species in some details of organisation. With some 

 hesitation I have decided to identify them with Heller's Ascidia depressiuscula 

 obtained in Ceylon by Schmarda. The external appearance agrees fairly well with 

 Heller's figure (' Sitzb. Akad. Wiss. Wien.,' Jahrg. 1878), and the internal structure 

 does not differ from Heller's brief description except in regard to the number of 

 tentacles. 



The very small number of species of the large and usually abundant genus Ascidia 

 found in the Ceylon collection is remarkable, especially when we remember that 

 Sluiter describes no less than 24 species ot Ascidia (11 of them new to science) in 

 the results of the " Siboga " expedition through the Indian Archipelago further east. 



Ascidia (?) mikrenterica, Sluiter Plate I., figs. 38 and 39. 



There is a single specimen of an Ascidia with a thick sandy covering, obtained at 

 Station LXIL, 13 fathoms, which I refer with some doubt to this species. It has 

 been torn open, probably by the dredge when captured, and the anterior end is 

 absent. In the thick coating of sand, and in the i"elatively minute alimentary canal 

 (fig. 38), it resembles the "Siboga" species, but the structure of the branchial sac 

 (fig. 39) is different. However, I have seen so many abnormal branchial sacs, or 

 portions of branchial sacs, amongst known species that I cannot attach much 

 importance to the reduced size and number of the stigmata seen in this specimen. 



Ascidia polytrema, n. sp. Plate I., figs. 34 to 37. 



External Appearance. Oblong-ovate, with the posterior end rounded, the branchial 

 aperture on the anterior end and the atrial projecting from the dorsal edge about one- 

 third of the way back (fig. 34), Surface sandy ; size, 3*3 centims. x l'G centims. 



Test thin, with large grains of sand and shell fragments embedded in it. 



Mantle thin and weak ; delicate muscle bundles running transversely (fig. 36). 



Branchial Sac exceedingly thin and delicate. Internal longitudinal bars bearing 

 slight papillae. Meshes about square, with four stigmata in each. Occasional 

 horizontal membranes cross the meshes (fig. 37). 



Dorsal Lamina with slight ribs and minute marginal denticulations. 



